Guide to Moisture Meters

Moisture meters are an essential instrument used to detect moisture content in materials in many industries. Home and building inspectors rely on moisture meters to identify potential problems and damage to structures from moisture buildup. Woodworking industries such as furniture makers will use wood moisture meters to insure a quality product, and flooring contractors use moisture meters for determining ideal conditions when installing a floor over a concrete slab or sub floor.

The indicator scales on moisture meters can vary in appearance but similarly all will indicate moisture content in percent (% MC). While some moisture meters offer an analog scale, others will read %MC digitally. The accuracy of the %MC readings as well as the appropriate substrate scales vary per meter and can vary by brand and type.

Most moisture meters are calibrated to wood, which provides a relatively accurate reading in wood moisture content, typically this scale ranges in the 5-40% range. When testing the moisture content in non-wood materials, such as concrete a relative scale of 0-100 is often used, where 0 is bone dry and 100 is saturated. This is a relative scale, and moisture meters include visual LED indicators related to the percent reading on the scale for dry, moderate and saturated or wet readings. Additionally, some meters will also offer a third scale for readings for gypsum where the scale readings can range from 0.2% - 50% moisture content. When selecting a moisture meter for sheetrock it is advised that a moisture meter that offers a scale reading for gypsum be used.

Color indicators on moisture meters are helpful in determining whether the material being tested is considered dry versus a potential problem with moisture. The green (dry), yellow (moderate) and red (high) indicators typically identify where on the scale of %MC, the readings occur. This can clear up confusion where one interprets a %MC as dry versus one that is moderate and may require more thorough investigation to determine if a problem with moisture in the material exists, especially if a visible sign of moisture does not exist.

3 Types of Moisture Meters

There are three common types of moisture meters used for the inspection of building and structure materials, pin-type, non-invasive, and meters that offer both pin-type and non-invasive, all-in-one meter. All three moisture meters offer specialized purpose and are unique to the end users application in determining moisture content (%MC) in materials.

Pin-type Moisture Meter

The first of these three meters is the pin-type. Pin type moisture meters will measure %MC at the depth of the head of the contact pins. Pin-type moisture meters have 2 pins on the instrument used to penetrate into the test surface at a desired depth. The reading of %MC is determined by measuring the electrical resistance between the tips of the 2 pins. This method of inserting pins into a surface is often viewed as an invasive process for measuring %MC. Typically these moisture meters will read up to 5/16” depth.

Pin-type meters use the principle of electrical resistance, to measure the moisture content in materials by measuring the conductivity between the pins. The tip of the pins are relatively sharp, un-insulated and are for penetrating into the surface for a sub-surface reading. With pin-type meters you can also obtain a reading by touching the pins to the surface for testing. Most pin-type moisture meters use a scale calibrated to wood, however this does not mean that the meter cannot be used to measure moisture in other substrates and materials. This type of moisture meter can also be used for, but is not limited to concrete, drywall, ceiling tiles, and painted surfaces. When using the wood scale on a pin-type moisture meter the %MC reading can range from 5% to 40% in moisture content. Generally the low end of this reading falls into the 5%-12% range the moderate range will be 15% to 17% and the high or saturated range will read above 17%. Scales for MC% ranges are provided in the instrument instructions and should be consulted concerning measuring ranges for particular surface materials.

Pin-type Moisture Meter

Pin type moisture meters are useful in measuring %MC in wood flooring, drywall, painted surfaces (such as the exterior of the home) carpeting, ceiling tile, and cement. A pin type moisture meter is the best way to identify the exact location of moisture buildup. A pin-type meter uses two pins that penetrate into the test surface at the users’ desired depth. When insulated contact pins are used, only the uncoated tips are exposed, providing an accurate reading of moisture content at various levels of penetration. Pin-type meters are the only instruments that allow the inspector to identify exact location of moisture at a given point. Using a pin-type meter is an effective way to determine the difference between shell and core moisture content. In some cases, the depth of the reading exceeds the length of the pin on the meter, if this is the case many meters are equipped with a connection option to add accessory probes that can be inserted further into a substrate for more accurate core or depth detection. An example would be for EIFS (Exterior Insulated Finish Systems) testing.

Pin-less Moisture Meter

Pin-less or non-invasive meters operate on the principle of electrical impedance.

This meter provides a non-destructive measurement of moisture in wood and other substrates such as concrete and gypsum. A non-invasive moisture meter may also be called a non destructive or a pin-less moisture meter. Scales on these meters are similar to that of the pin-type meters previously discussed, where the wood scale reads %MC 5-30% and non-wood materials %MC is read on a relative scale 0-100%.

This type of meter is commonly used to determine moisture content on a relative scale of 0-100% in concrete sub floors and flooring prior to laying a wood floor or other decorative flooring surface. Other common uses for a non-contact moisture meter for identifying possible moisture build-up behind bathroom/shower tiles, under vinyl flooring, and other finished surfaces as well as determining if water-borne finishes are adequately dry prior to second application.

Pin-less Moisture Meter

Non destructive moisture meters are capable of reading up to ¾” depth into a subsurface. Non contact moisture meters are useful for detecting problem moisture buildup where visual indicators are non-existent.

Pin-Type/Non-Pin Moisture Meter

A third and possibly more useful moisture meter would be a pin-style/non invasive all-in- one meter. This type of meter utilizes both methods for measuring MC% in surfaces. Because this type of meter offers the option to measure moisture content in substrates using both methods of reading moisture, one meter may be able to identify problem areas and then also be used to pinpoint the exact location where moisture damage or buildup is occurring. Essentially, this type of meter would utilize the same scales of MC% for wood and non-wood substrates, and allow the end user the versatility necessary for a full inspection in determining areas where moisture is an issue.

Pin-less Moisture Meter

Ideally, due to its diversity, this type of meter could be utilized by the flooring specialist, IAQ specialist, general contractor, and inspector.

Accessories for additional monitoring capability

Generally, pin-style and pin-less meters will provide moisture readings limited in depth. However, in some applications readings of moisture deeper than ¾” or 5/16” are necessary. In cases where depth measurements exceed that of a typical moisture meter, it is good to consider a meter that will accept an attachment for EIFS, deep penetration, or remote testing.

For deep penetration, long insulated contact pins may be used to obtain a moisture content measurement taken at depth. Holes may need to be drilled into the surface for testing and then the extra deep pins will be inserted into the pre-drilled holes and MC% measurement will be taken at the tip of the pins where they are not insulated. Insulating all but the tips of these pins will avoid a false moisture content reading and provide a more accurate reading just at depth where the tips of the pins are exposed.

In order to obtain a depth without drilling holes into the surface, a hammer probe can be used to insert a long pin into a wood surface for ½” up to 1-1/2” depth readings.

  • Use to measure moisture content in wood at different levels of penetration
  • Ideal for shell and core tests to detect moisture gradients and to test lumber with wet surfaces.

Moisture problems in exterior insulation and finish systems (EIFS) are typically found within stucco surfaces and stem from poor sealant application around window and door frames, or a result of faulty flashing installation. EIFS probes are used to test for MC% within these structures. An example of an insulated EIFS Probe for this specialized application is shown here:

EIFS Probe

Other applications may require measuring MC% on surfaces that are out of reach or in a relatively inaccessible area, such as under sinks or in ventilation areas, if this is the case, then using a pin-type moisture meter attachment may come in handy so the reading can still be obtained on the meter while the measurement is being taken at the source. Not all meters offer attachment ports for remote testing, EIFS testing or deep penetration. Typically this is an optional feature built into the model of moisture meter.

Commonly Asked Questions

Q. How do I care for my moisture meter?
A.

Moisture meters used for inspection, are generally factory calibrated. To keep your meter in good working condition;

  • Store the meter in a clean dry location
  • Change batteries and pins as needed; running a moisture meter on low batteries may cause the meter to go out of calibration.
  • Keep the electrodes and meter clean by using a biodegradable cleaner, using sparingly on external parts only.

If repairs or re-calibrations must be done on the meter, it is suggested to return the meter to the manufacturer or manufacturer service center for service and re-calibration to original standards.

Q. What type of meter works best for water-damaged structures?
A.

To quickly identify wet areas in walls and floors, pinless meters are easy to use. They offer the convenience of testing a large area quickly, and help you determine if further testing is required in certain spots.

A pin type meter, on the other hand, is the best way to identify the exact location of water damage behind walls, in sub-floors, or in any other area where moisture may be hidden behind another surface. The key to finding hidden moisture is to use an electrode with insulated contact pins. These pins read only at their un-insulated pin tips, allowing the user to drive the pins into material at various depths, noting readings at each level of penetration.

Q. How far should I drive non-insulated pins into wood?
A.

Drive pins into the wood at full depth if possible. At moisture levels below 10% it is essential to make positive contact with the substrate to get an accurate reading.
Q. Can I use a moisture meter to check for pest infestation?
A.

Yes -- a few meter readings in key locations of the structure will quickly indicate if the areas are safe or in danger of infestation. Using pin-type meters for pest control applications as the best way to identify the exact point of infestation behind walls and ceilings. The key to finding hidden moisture is to use an electrode with insulated contact pins. These pins read only at their un-insulated pin tips, allowing the contractor to drive the pins into material at different depths, noting readings at each level of penetration. A pinless meter is a good way to identify infested areas, as long as you do not have to penetrate into a hidden material.

Sources for More Information

For more information on moisture meters and their application and use;

www.delmhorst.com

www.gesensing.com

www.tramexltd.com

Please Note: The information contained in this publication is intended for general information purposes only. This publication is not a substitute for review of the applicable government regulations and standards, and should not be construed as legal advice or opinion. Readers with specific questions should refer to the cited regulation or consult with an attorney.